The present invention relates to a polyvinyl chloride-based unplasticized molding composition comprising, per 100 parts by weight of plastic, more than about 70% by weight, preferably more than about 85% by weight (relative to plastic), of vinyl chloride homo-, co- and/or ter-polymer and/or mixtures or alloys of vinyl chloride homo-, co- and/or ter-polymer having a vinyl chloride or PVC content of more than about 70% by weight, preferably more than about 85% by weight, and about 15 to 0% by weight of at least one impact-modifying polymer, or of the corresponding monomer component in the case of copolymers, selected from the group comprising alkyl acrylates, chlorinated polyethylenes, ethylene-vinyl acetate copolymer or ethylene-vinyl acetate-carbon monoxide terpolymer and other additives, processing auxiliaries and the like. According to the present invention, the polyvinyl chloride-based plastic molding composition includes a certain amount of parts by weight of at least one co-stabilizer, at least one surface-treated alkaline earth metal oxide and/or at least one partially hydrated alkaline earth metal oxide and other additives.
The invention furthermore relates to a process for the preparation of the molding composition and the use thereof for extrusion.
EP-B-0,001,859 discloses a rigid, heat-stabilized composition based on vinyl chloride polymers which includes as heat stabilizers magnesium oxide and a saturated polyhydric aliphatic alcohol and also calcium stearate and zinc stearate and other processing auxiliaries and additives. These heat-stabilized compositions are particularly suitable for the preparation of pipes and profiles. They have the advantage that they are lead-free and cadmium-free. However, the heat stability and processing properties of these compositions are in need of improvement.